Several species of animals have survived the breathing of various structures of oxygen-equilibrated perfluorinated liquids. Breathing certain oxygen-saturated liquids may be useful in the treatment of respiratory distress in infants and in cystic fibrosis. Such perfluorinated liquids have low viscosities and surface tensions and do not dissolve lung surfactant. They can be made radiopaque by slight alterations in their chemical structure and may therefore be useful in the diagnosis of lung disease and cancer. The purpose of the present research is to design, synthesize, and evaluate a number of liquids which can be safely breathed for diagnostic and therapeutic purposes. Studies are being made of the use of these substances as means to lavage the lungs and to fill alveoli so they will not collapse. The compounds are being tested as solvents for oxygen and carbon dioxide, for their ability to support respiration, and for their effects on the ultrastructure of the lung as judged by light and electron microscopy. BIBLIOGRAPHIC REFERENCES: Clark, Leland C., Jr., Eugene P. Wesseler, Samuel Kaplan, Marian L. Miller, Charles Becker, Carolyn Emory, Lilam Stanley, Fernando Becattini and Virginia Obrock. Emulsions of perfluorinated solvents for intravascular gas transport. Federation Proceedings 34, 1468-1477 (1975). Clark, Leland C., Jr., Eugene P. Wesseler, Samuel Kaplan, Robert Moore, Donald Denson and Carolyn Emory. Intravenous infusion of cis-trans perfluorodecalin emulsions in the rhesus monkey. In: Biochemistry Involving the Carbon-Fluorine Bond, edited by Robert Filler: American Chemical Society Symposium Series, No. 28, Chapter 8, Washington, D.C., 135-170 (1976).